Pickets are indispensable when building your pond. Using the poles you plot the circumference of your pond in the garden. This is also possible with a garden hose. Because the poles can be firmly anchored in the ground, the method with the poles is more effective. Also they can be used to level the pond. Subsequently you stretch a rope between the poles so that you can dig the pond edges off straight down. You can also imagine how your pond will look like and if the place you have chosen is the right one.
If necessary, the poles can be connected with each other by synthetic or wooden slats in order to a firm pond edge.